1. Field of the Invention
The present invention relates to a method and apparatus for simultaneously cutting and supporting a parison by an upper and lower pair of chucks so as to obtain a predetermined length thereof, and for stretching longitudinally the cut parison as the parison is delivered to a mold.
2. Description of the Prior Art
Conventionally, in molten blow molding using a molten-state tubular member made of synthetic resin (hereinafter referred to as "parison"), a parison is provided by an extruding die having a substantially circular opening so as to produce a parison having a hollow cylindrical shape. Typically, the outer diameter of the parison must be less than the inner diameter of the mold. Thus, in the case of a bottle having a small diameter portion, the outer diameter of the parison must be very small. Such a small diameter is difficult to achieve, however, particularly because the diameter of the extruded parison increases due to the high pressure differential between the interior and exterior of the extruding die, etc. This unwanted swelling in the diameter of the extruded parison becomes more and more noticeable as the speed of extrusion is increased.
In view of this swelling problem, the extruded parison outer diameter is reduced by stretching the parison during the time it is moved from the extruder to the blow mold. One conventional apparatus using the stretching is a molding device of the vertically rotary type provided with molds arranged such that the base portions of each mold continuously are confronted with each other, or the molds are circumferentially disposed in parallel with extruded parisons. Another conventional apparatus using stretching is of the so-called "caterpillar type" molding device having molds disposed in oval rotaries and the extruded parisons are stretched during molding when two rotaries are confronted with each other at linear portions thereof. According to these two methods, the extruded parison diameter is reduced by holding and stretching the parison by means of a mold whose rotating speed is higher than the parison extruding speed. However, noticeable drawbacks are present because the longitudinal size of the mold is restricted and diameter reduction may be small if the mold size is small, resulting in restricting the length of the parison because the molds are arranged in a longitudinal direction. On the other hand, a conventional horizontal rotary type molding device is provided having molds which are vertically and circumferentially disposed. The parisons are downwardly and vertically extruded from the extruder and are directly held by a rotating mold. In such apparatus, however, the parison diameter increases, and it is difficult to perform blow molding for small diameter portions of the bottle without cutting the parison.